The present invention relates to communications networks including mobile asynchronous transfer mode (ATM) and Internet-Protocol (IP) networks. More particularly, the invention relates to route optimization and handoff management in communication networks.
The term xe2x80x9cnetwork node,xe2x80x9d as used herein, is a system in a communications network that performs a switching or routing functions. A network node can be an access node if it has links to endpoints (users). A network node can be a transit node if all it slinks are to other network nodes with no links to endpoints. Examples of network nodes are ATM switches, IP routers, SONET crossconnects, telephony switches, WDM (Wavelength Division Multiplexed) optical crossconnects and other similar systems.
An network node can be an xe2x80x9coriginating network nodexe2x80x9d (the network node from which a communication path originates; a xe2x80x9ccurrent-location network nodexe2x80x9d (the network node to which a mobile or remote user is currently connected to communicate with the originating network node); and a xe2x80x9cnew-location network nodexe2x80x9d (the network node to which the remote user will be handed off to).
In a mobile network, the term xe2x80x9cnetwork node,xe2x80x9d refers to an access point or a base station (which may include an ATM switch).
The term xe2x80x9cmobile user,xe2x80x9d as used herein, refers to a person connected to (or who will be connecting to) a current-location network node to establish communication with the originating network node.
The term xe2x80x9ccall,xe2x80x9d as used herein, refers to any connection (e.g., voice, data, etc.) between an originating party and a receiving party over a communication path.
The term xe2x80x9ccommunication path,xe2x80x9d as used herein, refers to the path from the originating party to the receiving party over the network.
The use of ATM and IP technology in mobile communication networks is becoming increasingly common. In mobile ATM networks, xe2x80x9chandoff proceduresxe2x80x9d and xe2x80x9clocation management proceduresxe2x80x9d are needed to support user mobility. Handoff procedures are needed to reroute connections of a call-in-progress when a mobile user is moving (and therefore changing the route that the call takes). Location management consists of tracking mobile users and locating them for delivering a yet-to-be-established incoming call to the mobile user. In both sets of procedures, paths taken by connections could become xe2x80x9csub-optimal,xe2x80x9d i.e., the paths taken may not be the best paths between the two endpoints of the connection.
Handoff management consists of procedures to reroute connections on which a mobile user is communicating while moving. If a connection exists between a first network node and a second network node, and mobile user moves to a third network node, connections need to be rerouted. Thus, a rerouting is required whether the mobile user which initiated the call moves, or the mobile user which received the call moves.
Various prior art schemes for handoff management are known and generally operate in one of two ways. A first method, called xe2x80x9cpath rerouting,xe2x80x9d is described with reference to FIG. 1A. By this method, a mobile user 110 using an connection 112 between an originating network node 114 and a nearby network node 116 is moving towards a different network node 118. The system recognizes the movement of the mobile user 110 and sets up a new connection 120 (shown in dotted lines) between originating network node 114 and the destination network node 118. Once the new connection 120 is established, the connection between originating network node 114 and the old network node 116 is dropped, with the communication by the mobile user 116 with originating network node 114 continuing in a virtually xe2x80x9cseamlessxe2x80x9d manner.
In the scheme illustrated in FIG. 1A, since the entire connection is being rerouted (i.e., there is no common path between the first connection 112 and the second connection 120), handoff latency is an issue. Considerable time and network resources are spent establishing the new connection 120 over an entirely new path before the old path can be dropped.
An alternative handoff method, called xe2x80x9cpath extension,xe2x80x9d is illustrated with reference to FIG. 1B. Under this method, the path 112 between originating network node 114 and the new network node 118 is established by simply extending a new path 122 (shown in dotted line) to the new network node 118 from the old network node 116, in a xe2x80x9cconnect-the-dotsxe2x80x9d fashion. Using this method, lower handoff latencies can be achieved because the old and new base stations are simply interconnected as needed. However, the path taken by the connection will often be sub-optimal, because the new path added on to the old one may follow a circuitous route.
Neither of the prior art handoff methods determine whether the route established between the originating point and the network node closest to the mobile user is optimal, nor do they optimize the connection path to establish such an optimal route.
Thus, there exists a need for a system which may provide an efficient handoff management scheme/method to optimize routes of connections such that an efficient usage of network resources results.
Two handoff schemes are disclosed herein. In a first embodiment a procedure for finding an optimal path between an originating network node and a destination network node is integrated in the handoff procedure. An optimally routed connection is obtained by first determining an optimal xe2x80x9ccrossover nodexe2x80x9d along the existing path and then the handoff is effected by altering the existing connection route so that it travels along the existing path until it reaches the crossover node, where the path then varies from the original route, and a new segment between the crossover node and the new location is established. Then the call is switched to the new segment and the corresponding old segment on the old connection is released.
In an alternative embodiment, the handoff procedure is performed first by completing a fast reroute connection using the prior art path extension method. This results in a quick, but sub-optimal handoff connection. Once the handoff is completed, the route is optimized by selecting a segment on the sub-optimal connection for rerouting and then utilizing the method of the first embodiment to establish an optimally routed connection.
The method of determining an optimal connection path and rerouting the existing connection path to this optimal connection path, as described in the first embodiment, is applicable to all communication networks deploying connection-oriented technologies. These communications networks include land-line networks and mobile networks.
Similarly, the method of route optimization for optimizing a suboptimal connection, as described in the second embodiment, is applicable to all communication networks deploying connection-oriented technologies. These communications networks include land-line networks and mobile networks.
Within communications networks, the kinds of networks to which the present invention is applicable includes flat networks, hierarchical networks, and PNNI-hierarchical networks.